LOS ANGELES, CA -- Parents like to think they know what their kids are doing on their smartphones and tablets, but children may be hiding their activities using secret apps.

When your kids are on their smartphone or tablet, do you have any idea what they're doing? Can you be sure they're not texting, downloading or contacting someone or something that could cause them harm?

Even if you check their devices, you may be missing something - because there are secret apps children know about but can hide from their parents.

"They're hiding pornography, they're hiding chats with other people. They're hiding things that actually they should be more aware are dangerous to these kids," said David Perry, one of the leading cyber security experts in the country.

Perry said some of the popular secret apps like Calculator %, Kycalc or Best Secret Folder are disguised as fully functional calculators. But when a secret pass code is entered, it unlocks a whole new gateway for your child, allowing them to store photos and text messages they don't want you to see.

"If they've gone to a porn site and they've been infiltrated, then it's possible that bad guys are tracking their every move," Perry said. "By the time they get their driver's license, they will already be 'owned,' as we say in the hacker world."

Sue Laird of Huntington Beach is extremely cautious about what her child is logging into, even restricting the use of devices. Still, her daughter Kayce goes on chat rooms with her friends.

"Georgia is one new friend that she's found. She truly believes it's an 11-year-old girl in Georgia, but is it really?" Laird said. "We have no way of really knowing."